Simmons, 24, is Watson's costar in the recently wrapped flicked "The Perks of Being a Wallflower." According to an eyewitness, Simmons dropped off Watson at the eatery to dine with some friends and they parted ways very reluctantly.

The pair "looked very loved-up," the observer tells Us Weekly. "Holding and hugging each other for a while and playfully kissing. [They] seemed very open and not trying to hide their affection."

Watson and Simmons have been snapped together before, working out and giggling together in rural Pennsylvania in May, where "Wallflower" was filmed. Simmons was constantly by Watson's side at an MTV Movie Awards afterparty June 6. At that bash, Simmons even grabbed Watson's bottom during their affectionate night out together, according to a fellow partygoer.

Who is Simmons, anyway? Raised in Dallas, Texas, the cute actor has plenty of film credits to his name, including "Scott Pilgrim vs. the World," 2009's "Jennifer's Body" (co-starring Megan Fox), and 2007's "Evan Almighty."